Network for connecting a plurality of nodes using a plurality of channels

Abstract: In a network system, a loop-shaped transmission path is constituted by multiplexing a plurality of loop-shaped transmission channels. A plurality of nodes are connected to the loop-shaped transmission path. Each of the plurality of nodes can access at least two channels of the plurality of channels multiplexed in the loop-shaped transmission path. Each of plurality of nodes has a loop-shaped transmission route which is formed via a plurality of channels and which does not exceed one round of the loop-shaped transmission path.

Description: The present invention relates to a network for connecting a plurality of nodes using a plurality of channels. Most of conventional networks having a plurality of channels are constituted by a plurality of unidirectional or bidirectional channels and a plurality of nodes for accessing all these channels to transmit/receive data. In such a network, high-speed, large-capacity data transfer can be realized using a plurality of channels. On the other hand, since each node must execute transmission/reception processing for all channels, processing cost is high, and the node arrangement tends to be complicated since it requires a large number of transmitters and receivers, and the like. In order to eliminate the above-mentioned drawbacks, a system for regularly selecting channels to be accessed by nodes to decrease the number of channels to be accessed by each node to be smaller than the total number of channels has been proposed. A system, disclosed in Japanese Laid-Open Patent Application No. 64-24539 as an example of the above-mentioned system, has a unidirectional loop-shaped transmitting path obtained by multiplexing d k (d and k are natural numbers equal to or larger than 2) channels having the same transmission direction, and each node is arranged to access d channels which are regularly selected. In this arrangement, when packet transmission is performed between arbitrary nodes, an intermediate node located at an intermediate position between transmitting and receiving nodes selects a channel for transmitting a packet in accordance with a proper routing algorithm, and repeats and transfers the packet, thus realizing a communication even when the transmitting and receiving nodes do not access the same channel. Fig. 1 shows the arrangement of the conventional system when the number of channels to be multiplexed is 8, and the number of channels to be accessed by each node is 2 (i.e., d = 2 and k = 3). Referring to Fig. 1, loop-shaped channels 101 to 108 have a counterclockwise transmission direction in Fig. 1. Each of nodes 109 to 144 is connected to two channels indicated by marks ○. In this conventional system, since the number of channels to be accessed by each node is small, the node arrangement can be simplified. However, the average transmitting route length of a packet from a transmitting node to a receiving node is always more than half a round of the transmitting path in the case of a uniform traffic distribution. Furthermore, in terms of the characteristics of the network arrangement, the transmitting route length from a given node to a near node particularly becomes as large as one round or more of the transmitting path. For example, when the transmitting node is the node 109 and the receiving node is the node 110 adjacent to the node 109, an example of the shortest transmitting route is one which regenerates data from the transmitting node 109 via the intermediate nodes 113, 117, 121, 125, 129, 133, 137, and 143, and reaches the receiving node 110, and this transmitting path becomes more then one round of the transmitting path (in this case, data is transmitted from the node 109 to 137 using the channel 101, changes the channel to the channel 103 at the intermediate node 137, and thereafter, is transmitted to the receiving node 110 using the channel 103). Similarly, when the transmitting node is the node 109, the transmitting route length becomes more than one round of the transmitting path when the receiving node is the node 111, 112, 115, or 116. Such an increase in transmitting route length leads to an increase in transmission delay time of a packet, and disturbs improvement of the throughput of the network. The following network will be described as the second prior art. A Manhattan street network announced by Maxemchuk in "The Manhattan street network", Proc. GLOBECOM '85, New Orleans, pp. 255- 261 (1986), can be applied from a small-scale network to a large-scale network, and various examinations have been made. In the Manhattan street network as this prior art, as shown in Fig. 2, a plurality of nodes 206, 207,..., 241 are arranged in a two-dimensional matrix and are connected via a plurality of vertical loop-shaped transmitting paths 242, 243, 244, 245, 246, and 247, and a plurality of horizontal loop-shaped transmitting paths 248, 249, 250, 251, 252, and 253. The transmission directions of these vertical and horizontal transmitting paths are reversed every other path. In this prior art, the presence of a route for transmitting information from an arbitrary node to another arbitrary node is guaranteed. The repeating and route selection operations for information transmitted from a transmitting node are realized by nodes on the route to transmit the information to a target receiving node. However, in the above-mentioned prior art, in order to connect N nodes, loop-shaped transmitting paths as large as 2 N paths are required. For this reason, laying, maintenance, and management of the network are complicated. As the third prior art for solving the above-mentioned problem, a prior art for one-dimensionally arranging nodes using a cable such as a multi-core optical fiber which bundles a plurality of transmitting paths while maintaining the logical connection relationship among nodes of the Manhattan street network is known. Fig. 3 shows the above-mentioned third prior art, and illustrates the arrangement for connecting 36 nodes using a 12-core optical fiber. In Fig. 3, only 18 nodes are illustrated. Referring to Fig. 3, first, second, third, fourth, fifth, and sixth cores 254, 255, 256, 257, 258, and 259 of the optical fiber respectively correspond to the vertical loop-shaped transmitting paths 242, 243, 244, 245, 246, and 247 in the second prior art, and seventh, eighth, ninth, 10th, 11th, and 12th cores 260, 261, 262, 263, 264, and 265 respectively correspond to the horizontal loop-shaped transmitting paths 248, 249, 250, 251, 252, and 253 in the second prior art. In the third prior art, complexity associated with laying, maintenance, and management of the transmitting path can be improved slightly. However, an optical fiber which has cores as large as 2 N cores must be used for N nodes. As a method of solving the problem of the third prior art, it is possible to realize the system of the third prior art using a single-core optical fiber by optical wavelength multiplexing using a plurality of transmitting wavelengths, Fig. 4 shows an example of the arrangement of a network constituted by 16 nodes 274 to 289 using eight independent wavelengths λ 1 to λ 8 266 to 273. Each node transmits/receives light components of only two designated wavelengths indicated by marks ○. In this case, the wavelengths are selected so as not to interfere with each other in transmission/reception using different wavelengths. In this arrangement, a plurality of channels constituted by the multi-core optical fiber in the third prior art are replaced by channels using light components of different wavelengths. In this manner, the Manhattan street network can be realized by using a single-core optical fiber. However, in this case, a wavelength-multiplexed transmitting path having wavelengths as large as 2 N wavelengths must be constituted for N nodes. In addition, the arrangement of each node used in this network is not known. Furthermore, the publication "Routing in the Manhatten Street Network" by N.F. Maxemchuk, in IEEE Transactions on Communications, Vol. 35, No. 5, May 1987, New York, US, pages 503-512, discloses a Manhattan Street Network (MSN) arrangement, in which first transmission direction channels and second transmission direction channels are arranged in a lattice configuration, wherein a node is disposed at each of crossing points in the lattice configuration. Such an arrangement, however, leads to a large number of channels being required for communication via said MSN network. Consequently, it is an object of the present invention to provide a network which is free from the above mentioned drawbacks, and in particular to provide a network having a more simple network configuration and which requires less channels, as compared to the MSN network known from the above referenced publication. According to the present invention, this object is achieved by a network according to claim 1. Advantageous further developments of the present invention are as set out in the respective dependent claims. Fig. 1 is a schematic view showing the arrangement of a network of the first prior art; Fig. 2 is a schematic view showing the arrangement of a network of the second prior art; Fig. 3 is a schematic view showing the arrangement of a network of the third prior art; Fig. 4 is a schematic view showing the arrangement obtained when a wavelength-multiplexed system is adopted in the third prior art; Fig. 5 is a schematic view showing the arrangement of a network according to the first embodiment of the present invention; Fig. 6 is a block diagram showing the arrangement of a node used in the network of the present invention; Fig. 7 is a block diagram showing another arrangement of the node used in the network of the present invention; Fig. 8 is a block diagram showing the arrangement of a connection means used in the first embodiment; Fig. 9 is a block diagram showing the arrangement of a connection means used in the second embodiment; Fig. 10 is a schematic view showing the arrangement of a network according to the third embodiment of the present invention; Fig. 11 is a block diagram showing the arrangement of a connection means of the third embodiment; Fig. 12 is a schematic view showing another arrangement of a network of the first embodiment. (First Embodiment) Fig. 5 shows the first embodiment of the present invention. In this embodiment, a communication control means of the Manhattan street network can be used. Fig. 5 illustrates a connection example obtained when 36 nodes are connected via eight channels each of which forms a loop-shaped transmitting route and which are formed by multiplexing eight wavelengths in a single-core optical fiber ring. Fig. 5 shows only 24 nodes for the sake of simplicity. Fig. 5 illustrates nodes 501 to 524. Eighteen nodes including a subgroup of the nodes 501 to 506, a subgroup of the nodes 513 to 518, and a subgroup of nodes 525 to 530 (not shown) constitute a first node group. Other nodes constitute a second node group and similarly forms subgroups. Each node accesses two assigned channels indicated by marks ○ in Fig. 5, i.e., performs transmission/reception using two wavelengths. The internal arrangement of each of these nodes will be described later. Eight channels 537 to 544 are formed in a single-core optical fiber ring 557 using different wavelengths λ 1 , λ 2 , λ 3 , λ 4 , λ 5 , λ 6 , λ 7 , and λ 8 . In this case, as the wavelengths, λ 1 = 1.50 µm, λ 2 = 1.51 µm, λ 3 = 1.52 µm, λ 4 = 1.53 µm, λ 5 = 1.54 µm, λ 6 = 1.55 µm, λ 7 = 1.56 µm, and λ 8 = 1.57 µm are used. The channel 537 formed by the wavelength λ 1 corresponds to a first channel group (one channel in this embodiment), the channel 538 formed by the wavelength λ 2 corresponds to a second channel group (one channel in this embodiment), and the six channels 539 to 544 formed by the wavelengths λ 3 to λ 8 constitute a third channel group. Each channel in the third channel group can form a loop-shaped transmission route of itself. The transmission directions of the channels 539, 541, and 543 are the same as that of the first channel, and the transmission directions of the channels 540, 542, and 544 are the same as that of the second channel. The nodes in the first node group access the first channel, and the nodes in the second node group access the second channel. The subgroups in the first and second node groups access the channels in the third channel group, so that channels to be accessed by the nodes in each subgroup do not overlap each other. Furthermore, in Fig. 5, connection means 545 to 548 are used for connecting the first and second channels 537 and 538. Each of these connection means has a terminating function of receiving a transmission signal which is transmitted to the right (Fig. 5) at the wavelength λ 1 , transmitting the received signal in the opposite direction (to the left in Fig. 5) at the wavelength λ 2 , and preventing this optical signal from being transmitted to the right beyond the connection means, and also has a terminating function of receiving a transmission signal which is transmitted to the left at the wavelength λ 2 , transmitting the received signal in the opposite direction (to the right) at the wavelength λ 1 , and preventing this optical signal from being transmitted to the left beyond the connection means. These connection means are respectively arranged between the subgroups. The internal arrangement of each of these connection means will be described later. Fig. 6 shows the arrangement of a node such as the nodes 502, 504, 506, 507, 509, 511, 514, and the like according to the first embodiment of the present invention, each of which transmits/receives two wavelengths (λ r and λ e ) having different transmission directions. Referring to Fig. 6, the single-core optical fiber 557 serves as a transmission medium of the channels having eight wavelengths shown in Fig. 5. In Fig. 6, a filter A 559 is used for cutting off λ r and λ e as the wavelengths used in transmission/reception of the node, and for passing wavelengths other than λ r and λ e . The node comprises optical couplers A 558, B 560, C 561, and D 562. The optical coupler A 558 divides and outputs an optical signal input from the left (Fig. 6) to the compler A 559 and the optical coupler C 561. Also, the optical filter 558 multiplexes output light from the optical coupler C 561 with output light from the filter A 559, and outputs the multiplexed optical signal to the left in Fig. 6. Similarly, the optical coupler B has a function of dividing and outputting an optical signal input from the right in Fig. 6 to the filter A 559 and the optical coupler D 562, and a function of multiplexing output light from the optical coupler 562 with output light from the filter A 559, and outputting the multiplexed optical signal to the right in Fig. 6. The optical coupler C 561 has a function of outputting output light from the optical coupler A 558 to a filter B 563, and outputting output light from a transmitting unit A 564 to the optical coupler A 558. Similarly, the optical coupler D 562 has a function of outputting output light from the optical coupler B 560 to a filter C 566, and outputting an output from a transmitting unit B 565 to the optical coupler B 560. The filter B 563 has a function of passing only the wavelength λ r to be transmitted to the right of the transmitting/receiving wavelengths of the node indicated by marks ○ in Fig. 5, and cutting off all other wavelengths. Similarly, the filter C 566 has a function of passing only the wavelength λ e to be transmitted to the left, and cutting off all other wavelengths. Each of the transmitting units A 564 and B 565 has a function of converting an electrical signal output from a memory unit A 568 or B 569 into an optical signal having a predetermined wavelength (λ e or λ r ), and outputting the converted optical signal. Each of receiving units A 567 and B 570 has a function of receiving an optical signal output from the filter B or C, converting the optical signal into an electrical signal, and outputting the converted electrical signal. The memory units A 568 and B 569 are used for buffering an electrical signal output from an SW unit 571 as needed. When an electrical signal received by the receiving unit A 567 or B 570 requires repeating, the SW unit 571 refers to a repeating route and outputs the electrical signal to the memory unit A 568 or B 569. When repeating is not required, i.e., when the received signal is addressed to the self node, the SW unit 571 outputs the signal to an output unit 572. Furthermore, for an electrical signal output from an input unit 573, the SW unit 571 refers to a repeating route on the basis of the node number of a transmission destination, and outputs the electrical signal to the memory unit A 568 or B 569. The output unit 572 is used for connecting a signal transmitted to the self node to a required external device. The input unit 573 is used for inputting a signal output from the external device. Fig. 7 shows the arrangement of a node such as the node 501, 503, 505, 513, 515, 517, and the like according to the first embodiment of the present invention, each of which transmits/receives two wavelengths to be transmitted to the right in Fig. 7. Referring to Fig. 7, blocks denoted by the same reference numerals as those of the blocks in Fig. 6 provide the same functions by replacing λ r and λ e in Fig. 6 by λ r1 and λ r2 , respectively. In Fig. 7, an optical coupler E 574 divides light output from the optical coupler A 558, and outputs the divided optical signals to the filters B 563 and C 566. An optical coupler F 575 multiplexes optical signals output from the transmitting units A 564 and B 565, and outputs the multiplexed optical signal to the optical coupler B 560. The nodes 505, 510, 512, 520, 522, 524, and the like shown in Fig. 5 according to the first embodiment of the present invention are those for transmitting/receiving two wavelengths λ e1 and λ e2 to be transmitted to the left. Each of these nodes has an arrangement obtained by reversing the arrangement shown in Fig. 7 in the right-and-left direction, and by replacing λ r1 and λ r2 by λ e1 and λ e2, respectively. Fig. 8 shows the arrangement of each of the connection means 545 and 547 according to the first embodiment of the present invention. Referring to Fig. 8, blocks denoted by the same reference numerals as those of the blocks shown in Fig. 6 provide the same functions by replacing λ r by λ 1 as the first channel and λ e by λ 2 as the second channel. In the connection means with the arrangement shown in Fig. 8, an optical signal which is transmitted at the wavelength λ 1 from the left to the right in Fig. 8 is converted into a signal of the wavelength λ 2 , and the converted signal is transmitted to the left. On the other hand, an optical signal transmitted at the wavelength λ 2 from the right to the left is converted into a signal of the wavelength λ 1 , and the converted signal is transmitted to the right. Note that the arrangement of each of connection means 546 and 548 is the same as that shown in Fig. 8, and λ 1 and λ 2 are respectively replaced by λ 2 and λ 1 . The operation according to the first embodiment will be described below with reference to Figs. 5, 6, 7, and 8. In the following description, a case will be exemplified wherein a signal is to be transmitted from the node 507 to the node 524. The node 507 as a transmitting node has the arrangement shown in Fig. 6. In this node, a wavelength corresponding to λ r is λ 3 , and a wavelength corresponding to λ e is λ 2 . In the node 507, when a signal to be transmitted, which is added with transmission destination information, is input from the input unit 573, the SW unit 571 examines which of λ 2 and λ 3 is used for transmitting the signal. As the examination algorithm of this embodiment, a technique described in NICHOLAS, F, MAXEMCHUK, "Routing in the Manhattan street Network", IEEE TRANSACTIONS on COMMUNICATIONS, Vol. 35, No. 5, MAY 1987, pp. 503 - 512 can be used. With this technique, λ 3 is determined as the transmission wavelength. The output signal from the input unit 573 is input to the memory unit B 569 and is sequentially stored at the end of a memory queue. The transmitting unit B 565 converts an electrical signal output from the memory unit B 569 into an optical signal of the wavelength λ 3 , and sequentially outputs the converted signal to the optical coupler D 562. The optical signal of the wavelength λ 3 output to the optical coupler D 562 is output to the optical coupler B 560 to be multiplexed with optical signals of other wavelengths from the filter A 559, and is output onto the optical fiber 557 to propagate to the right in Fig. 6. The optical fiber 557 transmits optical signals of the wavelengths λ 1 , λ 3 , λ 5 , and λ 7 from the left to the right, and transmits optical signals of the wavelengths λ 2 , λ 4 , λ 6 , and λ 8 from the right to the left. These optical signals of different wavelengths are transmitted without disturbing other signals since they are not coherent with each other. The optical signals of the wavelengths λ 1 , λ 3 , λ 5 , and λ 7 output from the optical coupler B 560 of the node 507 are input to the neighboring node 508. The node 508 is a node for transmitting/receiving two wavelengths to be transmitted to the left, and has an arrangement horizontally symmetrical to that shown in Fig. 7. The optical signals of the wavelengths λ 1 , λ 3 , λ 5 , and λ 7 input from the right to the optical coupler B 560 of the node 508 are input to the filter A 539. In the node 508, as indicated by marks ○ in Fig. 5, λ e1 and λ e2 are respectively set to be λ 2 and λ 4 , and the filter A 559 is a filter for cutting off λ 2 and λ 4 . For this reason, the optical signals of λ 1 , λ 3 , λ 5 , and λ 7 pass through the filter A 559, and are input to the optical coupler A 558. Then, these optical signals are output to the neighboring node 509. The node 509 is a node for transmitting/receiving an optical signal of λ 5 to be transmitted to the right, and an optical signal of λ 2 to be transmitted to the left, and has an arrangement shown in Fig. 6. The optical signals of the wavelengths λ 1 , λ 3 , λ 5 , and λ 7 input to the optical coupler A 558 of the node 509 are divided by the optical coupler A, and are output to the optical coupler C 561 and the filter A 559. The optical signals of the wavelengths λ 1 , λ 3 , λ 5 , and λ 7 input to the optical coupler C 561 are output to the filter B 563. The filter B passes only the optical signal of the wavelength λ 5 , and cuts off other optical signals. The optical signal of the wavelength λ 5 passing through the filter B 563 is received by the receiving unit A 567, and is converted into an electrical signal. Thereafter, when the transmission destination node is the self node, the electrical signal is output to the output unit 572 via the SW unit 571. On the other hand, when the transmission destination node is not the self node, according to a predetermined algorithm, the electrical signal is stored in the memory unit A 568 or B 569, the electrical signal is converted into an optical signal of the wavelength λ 2 by the transmitting unit A 564 or is converted into an optical signal of the wavelength λ 5 by the transmitting unit B 565, and the converted optical signal is output onto the optical fiber 557 via the optical couplers C and A or the optical couplers D and B. The optical signals of the wavelengths λ 1 , λ 3 , λ 5 , and λ 7 , which signals propagate to the right, are input to the node 510. Since the node 510 is a node for transmitting/receiving two wavelengths (λ 2 and λ 6 ) to be transmitted to the left in the same manner as in the node 508, the optical signals of the wavelengths λ 1 , λ 3 , λ 5 , and λ 7 are divided by the optical coupler A 558 of the node 510. The signals divided and output in one direction are cut off by the filters B 563 and C 566. On the other hand, the signals divided and output in the other direction pass through the filter A 559, and are input to the node 511. The node 511 is a node for transmitting/receiving an optical signal of the wavelength λ 7 to be transmitted to the right, and an optical of the wavelength λ 2 to be transmitted to the left, and has an arrangement shown in Fig. 6. In the node 511, in the same manner as in the above-mentioned node 509, the optical signal of the wavelength λ 7 is converted into an electrical signal by the receiving unit 567, and thereafter, the electrical signal is transmitted from the transmitting unit A 564 as an optical signal of the wavelength λ 2 , is transmitted from the transmitting unit B 565 as an optical signal of the wavelength λ 7 , or is output from the output unit 572 depending on the transmission destination node information. In this manner, the optical signals of the wavelengths λ 1 , λ 3 , λ 5 , and λ 7 , which have been transmitted to the right via the nodes 507, 508, 509, 510, 511, and 512, are input to the connection means 546. At this time, the wavelength λ 3 corresponds to an optical signal transmitted from the transmitting unit of the node 507, and the wavelengths λ 5 and λ 7 respectively correspond to optical signals transmitted from the transmitting units of the nodes 509 and 511. In addition, the wavelength λ 1 corresponds to an optical signal transmitted from the transmitting unit of the connection means 545. The operation of the connection means 545 is the same as that of the connection means 547, as will be described later. The connection means 546 has an arrangement shown in Fig. 8. The connection means 546 receives an optical signal of the wavelength λ 1 to be transmitted to the right, converts the received signal into an optical signal of the wavelength λ 2 to be transmitted to the left, and transmits the converted signal to the left. In addition, the connection means 546 converts an optical signal of the wavelength λ 2 to be transmitted to the left into an optical signal of the wavelength λ 1 , and transmits the converted signal to the right. Furthermore, the connection means 546 terminates optical signals of the wavelengths λ 1 and λ 2 by cutting them off using the filter A 559, so as to prevent these signals from being transmitted to the right beyond the connection means. The optical signals of the wavelengths λ 1 , λ 3 , λ 5 , and λ 7 which are input to the optical coupler A 558 of the connection means 546 are divided, and are output to the optical coupler C 561 and the filter A 559. The optical signals of the wavelengths λ 1 , λ 3 , λ 5 , and λ 7 input to the optical coupler C 561 are output to the filter B 563. The filter B 563 passes only the optical signal of the wavelength λ 1 , and cuts off the remaining optical signals of the wavelengths λ 3 , λ 5 , and λ 7 . The optical signal of the wavelength λ 1 passing through the filter B 563 is received by the receiving unit A 567, and is converted into an electrical signal. Thereafter, the electrical signal is converted into an optical signal of the wavelength λ 2 by the transmitting unit A 564, and the converted optical signal is sent onto the optical fiber 557 via the optical couplers C 561 and A 558 as an optical signal to be transmitted to the left. In this manner, the optical signal of the wavelength λ 1 is converted into an optical signal of the wavelength λ 2 , and is transmitted in the opposite direction. On the other hand, of the optical signals of the wavelengths λ 1 , λ 3 , λ 5 , and λ 7 output from the optical coupler A 558 to the filter A 559, the optical signal of the wavelength λ 1 is cut off by the filter A 559, and only the optical signals of the wavelength λ 3 , λ 5 , and λ 7 are input to the optical coupler B 560. The optical coupler B 560 receives optical signals of the wavelengths λ 2 , λ 4 , λ 6 , and λ 8 to be transmitted to the left. And only the optical signal of the wavelength λ 2 is converted into an electrical signal by the receiving unit B 570, and the converted electrical signal is input from the transmitting unit B 565 to the optical coupler B 560 as an optical signal of the wavelength λ 1 via the optical coupler D 562, in the same manner as the optical signal to be transmitted to the left, which signal is input to the above-mentioned optical coupler A 558. In the optical coupler B 560, the optical signals of the wavelengths λ 3 , λ 5 , and λ 7 passing through the filter A 559 are multiplexed with the optical signal of the wavelength λ 1 output from the optical coupler D 562, and the multiplexed signals are output to the right. Similarly, of the optical signals of the wavelengths λ 2 , λ 4 , λ 6 , and λ 8 to be transmitted from the right to the left, which signals are input to the filter A 559, the optical signal of the wavelength λ 2 is cut off, and only the optical signals of the wavelengths λ 4 , λ 6 , and λ 8 pass through the filter A 559. These optical signals are multiplexed by the optical coupler A 558 with an optical signal of the wavelength λ 2 output from the optical coupler C 561, and the multiplexed signals are sent from the optical coupler 558 onto the optical fiber as optical signals to be transmitted to the left. The optical signals of the wavelengths λ 1 , λ 3 , λ 5 , and λ 7 to be transmitted to the right, which signals are output from the connection means 546, are input to the node 513. The node 513 is a node for transmitting/receiving optical signals of the wavelengths λ 1 and λ 3 to be transmitted to the right, and has an arrangement shown in Fig. 7. The optical signal of the wavelength λ 3 , which is sent from the node 507 and is addressed to the node 524, is regenerated by the node 513. The optical signals of the wavelengths λ 1 , λ 3 , λ 5 , and λ 7 input to the optical coupler A 558 of the node 513 are input to the optical coupler E 574, and are divided and output to the filters B 563 and C 566. The filter B 563 passes only the wavelength λ 1 , and cuts off the wavelengths λ 3 , λ 5 , and λ 7 . The optical signal of the wavelength λ 1 output from the filter B 563 is converted into an electrical signal by the receiving unit A 567, and thereafter, the electrical signal is processed by the SW unit 571 depending on the transmission destination node information, as described above. The filter C 566 passes only the optical signal of the wavelength λ 3 . This optical signal is converted into an electrical signal by the receiving unit B 570, and the electrical signal is output to the SW unit 571. In the description of this embodiment, since the optical signal of the wavelength λ 3 is sent toward the node 524, the SW unit selects λ 3 as the transmission wavelength, and writes the signal in the memory unit B. The signal addressed to the node 524 and written in the memory unit B is sequentially read out, and the readout signal is output from the transmitting unit B 565 to the optical coupler F 575 as an optical signal of the wavelength λ 3 . The optical coupler F 575 multiplexes the optical signal of the wavelength λ 3 with the optical signal of the wavelength λ 1 output from the transmitting unit A 564, and the multiplexed signals are output to the optical coupler B 560. Of the optical signals of the wavelengths λ 1 , λ 3 , λ 5 , and λ 7 to be transmitted to the right, which are output from the optical coupler A 558 to the filter A 559, the wavelengths λ 1 and λ 3 are cut off by the filter A 559, and only the wavelengths λ 5 and λ 7 pass through the filter A. The optical signals of the wavelengths λ 5 and λ 7 are multiplexed by the optical coupler B 560 with the optical signals of the wavelengths λ 1 and λ 3 output from the optical coupler F 575, and the multiplexed signals are sent onto the optical fiber 557 as optical signals to be transmitted to the right. The optical signals of the wavelengths λ 1 , λ 3 , λ 5 , and λ 7 to be transmitted to the right, which are output from the node 513 are input to the connection means 547 via the nodes 514, 515, 516, 517, and 518, as described above. In the connection means 547, an optical signal of the wavelength λ 1 to be transmitted to the right, which is output from the node 518, is transmitted as an optical signal of the wavelength λ 2 to be transmitted to the left, in the same manner as in the above-mentioned connection means 546. The optical signal of the wavelength λ 2 is converted again into an optical signal of the wavelength λ 1 to be transmitted to the right in the connection means 546, and the converted optical signal is received by the node 513. In this manner, a loop-shaped transmission route connecting the nodes 513, 514, 515, 516, 517, and 518 as a subgroup is formed. On the other hand, an optical signal, which is transmitted to the left from the node 519 to the connection means 547 at the wavelength λ 2 , is converted into an optical signal of the wavelength λ 1 to be transmitted to the right, and the converted signal is output. The optical signal of the wavelength λ 1 is transmitted from the connection means 548 as an optical signal of the wavelength λ 2 to be transmitted to the left, and is received by the node 524. In this manner, a loop-shaped transmission route connecting the nodes 524, 523, 522, 521, 520, and 519 is formed. Each of these loop-shaped transmission routes is formed by the two connection means and the first and second channels in all the subgroups. The optical signals of the wavelengths λ 1 , λ 3 , λ 5 , and λ 7 to be transmitted to the right, which are output from the connection means 547, are input to the node 519. The node 519 has the same node arrangement as that of the node 507, i.e., has an arrangement shown in Fig. 6. In the node 519, the optical signal of the wavelength λ 3 addressed to the node 524 is converted into an electrical signal by the receiving unit A 567, and the electrical signal is input to the SW unit 571. Since the destination node of the input signal is the node 524, the SW unit 571 selects λ 2 as the transmission wavelength, and writes the signal in the memory unit A 568. The signal addressed to the node 524 and written in the memory unit A 568 is converted into an optical signal of the wavelength λ 2 by the transmitting unit A 564, and thereafter, the converted optical signal is sent from the optical coupler A 558 onto the optical fiber 557 via the optical coupler C 561 as a signal to be transmitted to the left. The optical signal of the wavelength λ 2 , which is transmitted to the left from the optical coupler A 558, is multiplexed as an optical signal of the wavelength λ 1 to be transmitted to the right with the optical signals of the wavelengths λ 3 , λ 5 , and λ 7 in the connection means 547, as described above, and the multiplexed signals are sent into the optical fiber 557. The optical signals of the wavelengths λ 1 , λ 3 , λ 5 , and λ 7 to be transmitted to the right, which are sent into the optical fiber, are input to the connection means 548 via the nodes 519, 520, 521, 522, 523, and 524 in the same manner as in the operations in the above-mentioned nodes 507, 508, 509, 510, 511, and 512. The connection means 548 has an arrangement shown in Fig. 8. The connection means 548 receives only the optical signal of the wavelength λ 1 of the optical signals of the wavelengths λ 1 , λ 3 , λ 5 , and λ 7 to be transmitted to the right, and outputs the received signal as an optical signal of the wavelength λ 2 to be transmitted to the left in the same manner as in the connection means 547. In addition, the connection means 548 outputs the optical signals of the wavelengths λ 3 , λ 5 , and λ 7 to the right. At this time, the wavelength λ 1 corresponds to the signal addressed to the node 524, which signal is repeated by the node 519, and this signal is transmitted to the left at the wavelength λ 2 . The optical signal of the wavelength λ 2 is input to the left neighboring node 524 of the connection means 548. The node 524 is a node for transmitting two wavelengths λ 2 and λ 8 to be transmitted to the left, and its arrangement corresponds to one obtained by reversing the arrangement shown in Fig. 7 in the right-and-left direction. Of optical signals of the wavelengths λ 2 , λ 4 , λ 6 , and λ 8 to be transmitted to the left, which are input to the optical coupler A 558 of the node 524, the optical signals of the wavelengths λ 2 and λ 8 are converted into electrical signals by the corresponding receiving units, i.e., the optical signal of the wavelength λ 2 is converted by the receiving unit A 567, and the optical signal of the wavelength λ 8 is converted by the receiving unit B 570 in the same manner as in the node 508. These electrical signals are input to the SW unit 571. The electrical signal output from the receiving unit A 567 is the signal addressed to the node 524, which is transmitted from the node 507 at the wavelength λ 3 , is repeated by the node 513, is converted into an optical signal of the wavelength λ 2 by the node 519, is converted into an optical signal of the wavelength λ 1 by the connection means 547, is converted again into an optical signal of the wavelength λ 2 by the connection means 548, and is received by the node 524. In this manner, transmission from the node 507 to the node 524 is realized. Conversely, upon transmission from the node 524 to the node 507, various routes are available. For example, in one route, a signal is transmitted from the node 524 at the wavelength λ 8 , and is regenerated by the node 518. Thereafter, the wavelength is converted from λ 8 into λ 2 by the node 512, and the signal then reaches the node 507 via the nodes 511, 510, 509, and 508. As described above, in each subgroup, a loop-shaped transmission route can be formed. For this reason, the transmission route length between adjacent nodes is shortened. In this embodiment, each connection means has the terminating function. However, the connection means need not always have the terminating function. In this case, each node examines a destination node in units of data, and data of the first and second channel groups, which are input via the connection means, can be ignored. As described above, a Manhattan street network consisting of 36 nodes can be constituted using eight channels. In this embodiments, each of the first and second node groups are divided into subgroups which access a plurality of channels in the third channel group so as not to overlap each other, and the subgroups are connected via the connection means, so that the algorithm of the Manhattan street network can be used as a communication algorithm. However, the present invention is not limited to this. For example, a plurality of nodes each having a small transmission capacity may share a single channel in the subgroup, and a node having a large transmission capacity may access two or more channels in the third channel group. The connection means need not always be arranged in units of subgroups, but may be arranged in every other subgroups. Alternatively, if at least one connection means is arranged in the network, a loop-shaped transmission route can be formed by the first and second channel groups and the connection means in addition to that defined by the third channel group. (Second Embodiment) Fig. 9 shows the second arrangement of the connection means according to the present invention, i.e., the arrangement which facilitates acquisition of traffic information of the network as a whole and information associated with failures. In the arrangement of the connection means shown in Fig. 9, the SW unit 571, the memories units A 568 and B 569, the output unit 572, the input unit 573, which are the same as those in the node shown in Fig. 6, and a processing unit 576 for executing data processing are added to the arrangement shown in Fig. 8. In this arrangement, the nodes 501, 502, 503, 504, 505, and 506 transmit traffic information associated with themselves and information associated with failures toward the connection means 545 using the wavelength λ 1 , and the connection means 545 acquires these pieces of information. The acquired information is processed and summarized by the processing unit 576. The summarized information associated with the nodes 501, 502, 503, 504, 505, and 506 is transmitted toward the connection means 546 using the wavelength λ 1 again. In the connection means 546, information associated with the nodes 507, 508, 509, 510, 511, and 512 has already been summarized, and this information is processed together with the information from the nodes 501, 502, 503, 504, 505, and 506. In this manner, since each connection means acquires traffic information and failure information in units of nodes, which are sent from other connection means, the connection means can send an instruction for changing, e.g., the routing scheme in correspondence with these pieces of information to the respective nodes. (Third Embodiment) Fig. 10 shows the arrangement according to the third embodiment of the present invention. This arrangement is suited for a network which connects a large number of nodes by arranging a large number of sets of 24 nodes and two connection means in a loop pattern. Fig. 10 illustrates only one set for the sake of simplicity. Referring to Fig. 10, nodes 1076 to 1099 are arranged. Of these nodes, the nodes 1076 to 1087 constitute a first node group. In this group, the nodes 1076 to 1081 and the nodes 1082 to 1087 respectively constitute subgroups. Also, the nodes 1088 to 1099 constitute a second node group. In this group, the nodes 1088 to 1093 and the nodes 1094 to 1099 respectively constitute subgroups. The arrangement of each node corresponds to one of the arrangements shown Figs. 6 and 7, and the arrangement is horizontally symmetrical to that shown in Fig. 7 in correspondence with the transmission direction of a wavelength to be received. Each of connection means 1100 and 1101 has an internal arrangement shown in Fig. 11 (to be described in detail later). Channels 1102 and 1103 respectively formed by optical signals of wavelengths λ 9 and λ 10 constitute a first channel group. Channels 1104 and 1105 respectively formed by optical signals of wavelengths λ 11 and λ 12 constitute a second channel group. Channels 1106, 1107, 1108, 1109, 1110, and 1111 respectively formed by optical signals of wavelengths λ 13 , λ 14 , λ 15 , λ 16 , λ 17 , and λ 18 constitute a third channel group. Fig. 11 shows the internal arrangement of each of the connection means 1100 and 1101 used in the third embodiment of the present invention. Optical couplers A 558 and B 560 have the same functions as in Fig. 8. A filter D 1112 is a filter for cutting off and terminating optical signals of the wavelengths λ 9 , λ 10 , λ 11 , and λ 12 . An optical coupler E 1113 divides and outputs an optical signal output from the optical coupler A to filters E 1115 and F 1116. In addition, the optical coupler E 1113 multiplexes optical signals output from transmitting units C 1117 and D 1118, and outputs the multiplexed signals to the optical coupler A. An optical coupler F 1114 divides and outputs an optical signal output from the optical coupler B 560 to filters G 1121 and H 1122. In addition, the optical coupler F 1114 multiplexes optical signals output from transmitting units E 1119 and F 1120, and outputs the multiplexed signals to the optical coupler B 560. The filters E 1115, F 1116, G 1121, and H 1122 respectively pass optical signals of the wavelengths λ 9 , λ 10 , λ 11 , and λ 12 , and cut off other optical signals. The transmitting units C 1117, D 1118, E 1119, and F 1120 respectively convert electrical signals output from receiving units C 1123, D 1124, E 1125, and F 1126 into optical signals of the wavelengths λ 11 , λ 12 , λ 9 , and λ 10 , and output the converted signals. The receiving units C 1123, D 1124, E 1125, and F 1126 convert input optical signals into electrical signals. More specifically, wavelength conversion is attained by temporarily converting optical signals of λ 9 , λ 10 , λ 11 , and λ 12 input to the receiving units C, D, E, and F into electrical signals, and transmitting these electrical signals from the transmitting units C, D, E, and F as optical signals of λ 11 , λ 12 , λ 9 , and λ 10 . With this arrangement, this connection means serves as that for subgroups belonging to different node groups. In this embodiment, an optical signal of the wavelength λ 9 , which is output from the node 1081 to the right, and an optical signal of the wavelength λ 10 , which is output from the node 1087 to the right, are divided by the optical coupler A 558 in the connection means 1101, and are output to the filter D 1112 and the optical coupler E 1113. The optical signals of the wavelengths λ 9 and λ 10 divided and output to the filter D 1112 are cut off and terminated by the filter D 1112, and are never transmitted to the right beyond the connection means 1101. On the other hand, the optical signals divided and output to the optical coupler E 1113 by the optical coupler A 558 are output from the optical coupler E 1113 to the filters E 1115 and F 1116. The filter E 1115 passes only the optical signal of the wavelength λ 9 , and the filter F 1116 passes only the optical signal of the wavelength λ 10 . These optical signals are respectively converted into electrical signals by the receiving units C 1123 and D 1124, and the electrical signals are output from the transmitting units C 1117 and D 1118 as optical signals of the wavelengths λ 11 and λ 12 . The optical signals of the wavelengths λ 11 and λ 12 output from the transmitting units C 1117 and D 1118 are input to the optical coupler A 558 via the optical coupler E 1113 and are multiplexed with optical signals of other wavelengths from the filter D 1112. Thus, the multiplexed signals are output to the left. In this manner, optical signals, which are input to the connection means 1101 as optical signals to be transmitted to the right at the wavelengths λ 9 and λ 10 , are converted into the wavelengths λ 11 and λ 12 , and the converted signals are transmitted to the left. Thereafter, the optical signals are converted into optical signals of the wavelengths λ 9 and λ 10 in the connection means 1100 in the same manner as described above, and are output from the connection means 1100 as optical signal to be transmitted to the right again. In this manner, loop-shaped transmission routes are respectively formed by the nodes 1076, 1077, 1078, 1079, 1080, and 1081, and the nodes 1082, 1083, 1084, 1085, 1086, and 1087. At this time, a loop-shaped transmission route is formed by the channels using the wavelengths λ 9 and λ 11 and the connection means 1100 and 1101 in the subgroup of the nodes 1076 to 1081. A loop-shaped transmission route is formed by the channels using the wavelengths λ 10 and λ 12 and the connection means 1100 and 1101 in the subgroup of the nodes 1082 to 1087. These loop-shaped transmission routes are formed in all the subgroups. In this embodiment, since the number of channels in each of the first and second channel groups is two, and the channels in the first and second channel groups are respectively connected by the connection means, even if the number of connection means is decreased when the number of nodes is large, the algorithm of the Manhattan street network can be used. Since the number of channels in each of the first and second channel groups increases, the communication capacity can be increased particularly in the subgroup. In this embodiment, the number of channels in each of the first and second channel groups is two, but the number thereof is not limited to this. The number of channels in each of the first and second channel groups may be M (= integer), M connection means for connecting a single channel in the first channel group and a single channel in the second channel group to be 1 : 1 may be arranged in units of M subgroups, and each of the M subgroups may access the M channels in the first or second channel group. With this arrangement, a loop-shaped transmission route can be formed in units of the subgroups without being regenerated by another subgroup. The M subgroups between the two connection means may access one of the first and second channel groups as in this embodiment, or some of subgroups in the M subgroups between the two connection means may access the first channel groups and remaining subgroups may access the second channel group. At this time, if each subgroup alternately accesses the first or second channel group, the algorithm of the Manhattan street network can be used as in the first embodiment. In each of the above embodiments, a loop-shaped transmission route is formed within a subgroup in each of the first to third embodiments. With these arrangements, a communication can be performed between nodes relatively adjacent to each other without increasing a transmission distance. In each of the first to third embodiments, subgroups are divided to belong to first and second node groups. The first and second node groups respectively access first and second channels which have transmission directions opposite to each other. The loop-shaped transmission route in the subgroups belonging to the first node group and that in the subgroups belonging to the second node group have transmission directions opposite to each other. However, the present invention is not limited to this. For example, in the first embodiment, subgroups need not be divided into first and second node groups, and all nodes may access the first channel. Fig. 12 shows this arrangement. At this time, the algorithm of the Manhattan street network may be used as a communication algorithm modified in the transmission direction of a horizontal transmitting path, or another communication algorithm may be used. When nodes overlap to access a channel in a third channel group in each subgroup, the nodes may examine each signal destination address. In addition, a node having many signals to be transmitted/received may access a plurality of channels in the third channel group. Furthermore, the respective subgroups access the third channel group in the same pattern. That is, nodes at the same positions in different subgroups (e.g., positioning at the second node from the right) access the same channel in the third channel group. However, the present invention is not limited to this. A transmission route is easily set with nodes accessing in the same pattern regardless of using the algorithm of the Manhattan street network or not. (Another Embodiment) In each of the above embodiments, as an optical coupler of each node, an element for simply dividing or multiplexing optical signals has been exemplified. Alternatively, when an optical wavelength multiplexer/demultiplexer, a wavelength selection switch, or the like, which can separate only a specific wavelength may be used, wavelength filters after the optical coupler can be omitted. In each of the above embodiment, a plurality of channels are formed by wavelength multiplexing using an optical fiber. However, multiplexing is not limited to wavelength multiplexing. For example, a spatial multiplexing system using a bundle of a plurality of cables may be adopted. Also, a signal is not limited to an optical signal but an electrical signal or the like may be used. In this case, when signals are multiplexed by, e.g., frequency multiplexing, nodes and connection means can be connected using frequency filters, and the like. In each of the above embodiments, separate transmission media may be used without multiplexing a plurality of channels. In this disclosure, the term "transmission direction" does not mean a wiring direction when the network of the present invention is actually set, but means a logical direction when the arrangement of the network is one-dimensionally illustrated as in Fig. 5. Therefore, when separate transmission media are used without multiplexing a plurality of channels, a plurality of channels and a plurality of nodes may satisfy the access relationship of the network of the present invention.

Claims: A network comprising: a loop-shaped transmission path constituted by multiplexing a plurality of loop-shaped transmission channels ( 537, 538, 539-544 ), said plurality of channels being divided into a first channel group ( 537 ) consisting of at least one channel having a first transmission direction, a second channel group ( 538 ) consisting of at least one channel having a second transmission direction opposite to the first transmission direction, and a third channel group ( 539-544 ) consisting of at least one channel not belonging to said first and second channel groups; a plurality of nodes each of which accesses said first channel group and said third channel group; characterized by connection means ( 545-548 ) for outputting a signal inputted thereto from a channel belonging to said first channel group to a channel belonging to said second channel group, and for outputting a signal inputted thereto from a channel belonging to said second channel group to a channel belonging to said first channel group; and wherein a node group is constituted by a plurality of said nodes, said node group having two opposite ends, said connection means is arranged at both ends of said node group, and all of said nodes in said node group are connected to a loop-shaped transmission route formed of said connection means at both opposite ends of said node group and said channels of said first and second channel groups between said opposite ends, and wherein said node group is a first node group ( 501-506, 513-518 ), and said network further includes a second node group comprising a plurality of nodes each of which accesses at least one channel of said second channel group and at least one channel of said third channel group. A network according to claim 1, wherein said third channel group consists of at least one channel having the first transmission direction and at least one channel having the second transmission direction. A network according to claim 1, wherein at least one node of said node group can access each channel in said third channel group. A network according to claim 3, wherein a number of channels in each of said first channel group and said second channel group is M (with M being an integer), and the connection means for connecting said M channels in said first channel group and said M channels in said second channel group in a one-to-one manner is provided for each of M subgroups. A network according to claim 1, wherein said connection means includes stop means for stopping signals transmitted from the respective channels of said first channel group from being transmitted through the channels of said first channel group beyond said connection means and for stopping signals transmitted from the respective channels of said second channel group from being transmitted through the channels of said second channel group beyond said connection means.

Inventors: HATTORI JUN, YAMAMOTO MITSURU, HATTORI, JUN, YAMAMOTO, MITSURU, HATTORI, JUN, C/O CANON KABUSHIKI KAISHA, YAMAMOTO, MITSURU, C/O CANON KABUSHIKI KAISHA
Applicants: CANON KK, CANON KABUSHIKI KAISHA
Application year: 1994
Main classification: H04J14
IPC codes: H04L12, H04Q11, H04J14